Liquid‐Crystalline Biomineral Nanofibers: 1D Inorganic Materials with a High Aspect Ratio and Anisotropic Self‐Assembled Nanocomposites

In nature, shark tooth enameloid exhibits an intricate anisotropic structure composed of high-aspect-ratio fluorapatite (FAp) fibrous nanocrystals, which impart exceptional mechanical properties. Mineral-based liquid-crystalline (LC) colloids provide a promising strategy for constructing such anisotropic structural materials. However, fibrous nanoparticles with high aspect ratios are prone to irreversible aggregation and gelation due to their large surface area. Consequently, the development of 1D mineral-based LC colloids with a high aspect ratio (>100) is largely limited to clay, carbon, boron nitride, and metal oxide-based systems. Herein, LC FAp nanofibers (FApNFs) are demonstrated as environmentally friendly, biocompatible, and stimuli-responsive fibrous nanomaterials. Well-dispersed FApNFs are synthesized using an elongated acidic macromolecular template to control crystal morphology. Their atomic-scale structures, self-assembled behavior, and electro-responsive properties are described. These LC FApNFs exhibit macroscopic alignment in response to external electric fields. Unidirectionally aligned FApNFs are successfully immobilized within the hydrogel network, enabling the formation of anisotropic nanocomposite hydrogels. The FApNFs-based hydrogels exhibit pronounced anisotropic stiffness and toughness with orientational dependency. Owing to their facile preparation, eco-friendliness, and stimuli-responsive nature, LC FApNFs have potentials as bio-friendly functional materials.